This invention relates to matrix printing and, more particularly, to matrix printing using a printer of the type including a record material movable past a printing station, and a print assembly capable of printing a line of characters in dot matrix format upon relative movement of the print assembly and the record material.
There are a number of varieties of printers of the general type above described. First, there are serial matrix printers wherein the record material is moved in a first direction past the printing station, and the print assembly is capable of printing a line of characters sequentially (in series) in dot matrix format upon relative movement of the print assembly and the record material in a second direction perpendicular to the first direction. Typical serial matrix printers use a number of different types of print assemblies, such as wire-matrix print heads (e.g. ballistics heads of the type disclosed in U.S. Pat. Nos. 3,929,214 and 4,029,190) and ink jet heads.
A second variety of printers of the general type above described are line matrix printers, normally using an entire line's complement of print wires operated to print an entire line of characters simultaneously, as opposed to sequentially as in serial matrix printers. Ink jet printing assemblies could also be used in line printing.
An example of a serial matrix printer using a ballistics wire matrix print head is the Diablo Series 2300 matrix printer manufactured by Diablo Systems, Inc. of Hayward, California. A description of that printer appears in the Series 2300 Matrix Printer Maintenance Manual therefor which is contained in the file wrapper of the application, inasmuch as a preferred embodiment of the invention includes a number of components that are used in the Diablo 2300 printer.
Serial matrix printers, such as the Diablo Series 2300, may be operated at different carriage speeds in order to achieve different degrees of horizontal dot density. Typically such matrix printers use a 9-wire matrix head in order to form characters in a 7-dot column, 4-dot row matrix format when printing at speeds of about 200 characters per second (cps). If the hammer firing sequence for the print wires in the matrix head remains constant and the carriage printing speed is decreased to 100 cps, for example, the characters may be formed in a 7-dot column, 7-dot row, thereby significantly increasing the horizontal dot density and thus resolution of the printed information.
The capability of achieving higher dot densities when decreasing the carriage printing speed does not solve the problems of being able to print equally high resolution characters with angled portions, e.g. 45.degree. angled portions, such as is true with the letter "X". More specifically, slowing the printing speed to 100 cps would not contribute to a higher dot density and thus resolution along the 45.degree. angled lines. Only a greater horizontal dot density is possible, which would benefit such characters as the letter "E".
Very recently, a serial matrix printer has been introduced that has a high resolution printing capability for all characters. The printer is first operated at a constant speed (e.g. about 180 cps) from left to right, printing characters in a 7-dot column, 4-dot row matrix, as is conventional. However, then the record material is advanced a distance equal to a fraction, e.g. one-quarter, of the distance between adjacent dot centers in a vertical dot column, and the carriage is returned from right to left at the same speed, but this time printing some of the interspersed dots of the same characters. Two additional printing passes (left to right and then right to left) are accomplished with the record material being advanced additional quarter vertical dot spaces prior to each pass. The printing resolution is excellent in this four-pass system. However, in order to achieve a horizontal offset of the dots in each of the second through fourth passes consistent with the quarter vertical dot space advancement of the record material prior to each such pass, such being required in order to interspace dots along 45.degree. diagonal lines, it is necessary to use a relatively complex variable hammer firing system. Variation of hammer firing cycles between the different passes is required due to the fact that all four passes are accomplished at the same constant speed.
It would be desirable, therefore, to be able to print high resolution characters in accordance with a multi-pass printing system wherein the hammer firing sequence need not be varied, thereby preserving the relative simplicity of the hammer firing timing control.